Dielectric materials have high polarizability and are able to store electrostatic energy through charge separation of electric charges of opposite sign. Typically, capacitors are composed of metal electrodes or plates that are separated by a layer of dielectric material. An applied potential difference is used to ‘charge’ the capacitor by transferring electric charge from one electrode to the other. High voltage capacitors typically exist in cylindrical sandwiching of dielectric material and metal foil electrode. The dielectric material must be capable of holding an electric field across the electrodes without discharging it. When the electrical field within a dielectric medium changes, the momentary delay in change of the dielectric permittivity is referred to as the dielectric relaxation.
Commonly, dielectric materials have included inorganics such as mica and ceramics, although these materials suffer from brittleness and other insufficiencies. As a consequence, the use of polymeric materials has been explored, including high-polymer films such as polypropylene, polycarbonates, and polyimides. Enticing properties of such compounds include, for example, transparency, ductility, and low weight. Further polycarbonates are amorphous, glassy, non-crystalline materials ideally suited to film formation necessary for wound film capacitors. However, these materials often suffer from low glass transition temperatures making them impractical for many applications. Additionally, each type of material is limited by the temperatures at which it is able to sustain its breakdown voltage, inherent ability to be processed, and inherent dielectric permittivity. Commercial polycarbonate (BPA-PC) itself has been utilized many years in capacitors; however, it is desirable to develop polycarbonates with superior dielectric properties for use in energy dense capacitors. The use of polymeric materials with substitutions to the polymer backbone has been explored. For example, bis[4′-(3-fluoro-4-hydroxyphenyl)-phenyl]propane (DiF TABPA) has fluorine substituted onto the benzene rings located within the polymer backbone. See Bendler et al., Electrical Properties of a Novel Fluorinated Polycarbonate, 48 EURO. POLYMER J. 830-840 (2012). However, such compounds were found to either lack sufficient dielectric permittivity or to suffer from dielectric loss at temperatures that were too high, i.e., the loss would occur to close to room temperature. Substitutions of tethered nitrile groups onto the polymer backbone have also been explored. For example, 4,4-bis(4-hydroxyphenyl)pentanenitrile homopolycarbonate (CN-PC) was prepared and tested. See Bendler et al., Dielectric Properties of Bisphenol A Polycarbonate and Its Tethered Nitrile Analogue, 46 MACROMOLECULES 4024-4033 (2013). It was found that tethered nitrile groups created an encumbrance in rotation, which prevented adequate dipole rotation. Further, it was found that the nitrile substitutions were unable to exert the calculated effect of their dipoles, owing to restricted rotation on account of their size. Additionally, losses were into the working range of the capacitor.
Accordingly, it is an objective of the claimed invention to develop monomeric bisphenols containing one or more fluoromethyl groups in order to enhance the compounds dielectric constant.
A further object of this invention is to develop compounds having enhanced dielectric constants and low temperature dielectric losses suitable for pulsed power and other capacitors.
Still a further object of this invention is to dielectric materials, including, for example capacitors, comprising polycarbonates of homopolymers, copolymers, terpolymers, analogs, and/or other derivatives of bisphenols substituted with one or more fluoromethyl group; wherein such dielectric materials possess enhanced dielectric properties.